During his exile in Mexico, he participated in the preparations for the expedition of the boat Grandma to Cuba. When the Granma landing failed and the 82 expeditionaries were detected by government troops soon after, Raúl was one of only 12 fighters who managed to reach a safe haven in the Sierra Maestra mountains, forming the core of the nascent rebel army (see the Cuban Revolution). As Fidel's brother and trusted right-hand man, and given his proven leadership abilities during and after the Moncada attack, he was given progressively bigger commands.